U.S. Pat. No. 4,341,819, the teachings of which are described herein by reference, describes a coating powder which produces a wrinkle finish. The resin of this coating powder is epoxy, the cross-linking agent is methylenedisalicylic acid, and the cure catalyst borontrichloride ethylamine complex (BCl.sub.3 :NH.sub.2 Et). The selection of the methylenedisalicylic acid in this patent as the cross-linking agent is responsible for the wrinkled appearance of the fused and cured coating. Homologues of methylenedisalicylic acid were later found to be suitable, and in some cases preferable, for achieving a wrinkle finish, as described in U.S. Pat. Nos. 5,688,878 and 5,780,560, the teachings of each of which are incorporated herein by reference. Wrinkle finish epoxy resins are also described in U.S. Pat. No. 5,932,288, the teachings of which are incorporated herein by reference.
The coating powders described in the above-identified patents are primarily useful for coating substrates, such as metal, which are not heat sensitive. This is particularly true because in order that these coating powders produce a wrinkle finish, the curing must be conducted at relatively high temperatures, e.g., 375.degree. F. (191.degree. C.) or above.
Wrinkle finishes, such as are produced in the above-referenced patents, may be desired on heat-sensitive substrates, such as wood; wood products, including fiberboard, paper, etc.; and certain plastics. Accordingly, it is a general object of the present invention to provide coating powders which fuse and cure to provide wrinkle finishes at temperatures appropriate for the coating of heat-sensitive substrates.